Various uses of ATM are defined in specifications issued by 3GPP. Of particular relevance is 3GPP TS 25.433 V3.3.0, the contents of which are incorporated herein by cross-reference.
ATM is a connection-oriented technique, comprising the concatenation of ATM layer links required to effect end-to-end transfers between access points. Connection identifiers are assigned to each link of a connection as required and released when no longer needed. In general, signalling and user information are carried on separate ATM connections. In the ATM modes, data to be transmitted is organised into cells.
At a given interface, in a given direction, the different Virtual Path (VP) links multiplexed at the ATM layer into the same physical layer connection are distinguished by a VPI. The different Virtual Channel (VC) links in a Virtual Path Connection (VPC) are distinguished by a VCI.
The AAL (ATM adaptation layer) performs functions required by the user, control and management planes and supports mapping between the ATM layer and the next higher layer. The functions performed in the AAL depend upon the higher layer requirements.
The AAL uses the ATM layer service and includes multiple protocols to fit the need of different AAL service users:                AAL1 supports constant bit rate (CBR), connection-oriented, time-dependent data traffic (circuit, video signal and voice-band signal transport);        AAL2 is an ATM adaptation layer that supports variable bit rate (VBR), connection-oriented, time-dependent data traffic. AAL2 supports packetised voice and VBR video transmission;        AAL3/4 supplies sequencing and error detection support to variable bit rate (VBR), time-independent data traffic. Traffic can be both connection-oriented and connectionless (computer and network data transport, for example Frame Relay and SMDS); and        AAL5 supports variable bit rate (VBR), connection-oriented, time-independent data traffic (AAL5 does not support multiplexing, sequencing or error detection).        
Termination points are managed objects that terminate entities, such as trails and connections. Technology-specific termination points are derived using subclassing. In ATM switching a termination point can be at the virtual path or virtual channel level, and it can be external or internal.
In the presently proposed UTRAN specification, a traffic termination point is determined either when a radio link is set up for a dedicated channel or a common transport channel is set up for a common channel. Each radio link has a traffic termination point, and each transport channel within each radio link may have its own AAL2 termination point. Similarly, each common transport channel has its own AAL2 termination point. Once a traffic termination or AAL2 termination point is defined, it is fixed for the duration of the connection.
In a Node B element, this fixing of termination points can generate a resource fragmentation problem. This means that even though a particular Node B element can have theoretically sufficient capacity to accept a requested high bandwidth call (such as a video call), but will need to reject the call because the available resources are scattered.